The present invention relates, in general, to the use of electrophysiological monitoring devices, such as surface electromyography apparatus, to sense muscle loading, and more particularly, relates to the ergonomic design of the human operator interface of workstations at which workers perform repetitive tasks using such apparatus.
Repetitive tasks, for example, those performed in industrial or manufacturing settings at workstations, frequently cause worker injuries which are serious enough to result in the need for the worker to take sick leave and undergo physical and other medical and manipulative therapies in order to attempt to rehabilitate damage caused by chronic muscle overloading or fatigue. Neck, pectoral girdle, upper extremity, forearm, hand and back injuries regularly occur, with the result that the worker must seek medical assistance and the employer is faced with considerable worker downtime. Some professionals in the field worry that there is an epidemic of upper extremity work related repetitive motion disorders.
As part of the physical therapy for injured workers, physicians and allied health professionals may employ surface electromyography apparatus, including the affixation of sensing electrodes to the injured muscles and connective tissue so as to assist in the measurement of resting and active muscle tone. It has been discovered that excessive muscle tone, especially when performing repetitive tasks at manufacturing workstations, results in excessive levels of muscle loading, that in turn result in increased vulnerability to repetitive motion injuries. Such injuries almost exclusively occur in the cervical, pectoral girdle and upper extremity muscles, ligaments, tendons and connective tissue. Thus, a number of authorities are now calling these injuries, in deference to a lack of clear understanding regarding the etiology of these disorders, xe2x80x9cwork related upper extremity disorders.xe2x80x9d
The electrical input from the muscles to the surface electromyography unit, obtained via the sensing electrodes, allows one to visually observe the degree of both resting muscle tone and muscle loading when performing repetitive tasks. The muscles being measured by such apparatus are those that are determined by prior physical examination and ergonomic analysis to be most critically involved in the repetitive motion tasks the worker is performing at his workstation. The visual feedback offered by such measuring apparatus also enables the worker to observe the relationship between muscle tone and loading and his particular industrial injury and resultant pain syndrome. Recent research is validating that the retraining offered by this electromyographic xe2x80x9cbiofeedbackxe2x80x9d, in terms of its ability to promote and facilitate the workers learning of the voluntary ability to reduce muscle tone and task specific muscle loading, offers a pathway to the rehabilitation of the injured worker that results in improved recovery rates over and above that afforded by traditional physical and manipulative rehabilitative therapies.
The economic loss resulting from on-the-job injuries is more than the mere loss of man hours in that there is an associated reduction in worker morale that, in turn, reduces worker productivity. While electromyographic biofeedback therapy after an injury can reduce the number of further injuries to some degree, the repetitive nature of the tasks and the fact that nothing has really changed physically at the workstation, usually creates a high likelihood of the injury reoccurring.
The reoccurrence of such injuries and the associated psychological depression that accompanies them also can result in high worker turnover. Thus employers also are faced with reoccurring training costs, worker inefficiency and continuing poor worker morale.
One important approach to these problems is the ongoing effort on the part of industry to promote better ergonomic design of the human operator interface of manufacturing workstations. To this end, fixtures and jigs are provided which position workpieces in positions which are believed will allow the worker to perform the task with less muscle strain and stress, as well as enhance performance. Rests and tool support devices are also provided toward the end of reducing muscle fatigue.
The flow of workpieces through the workstation also will be designed to reduce worker manipulation of workpieces.
Such ergonomic designs, however, have largely been based on intuition, common sense and anecdotal experience, rather than any attempt to quantify the effects of workstation design on worker muscle loading. While current ergonomic workstation designs are a step forward, as compared to indifference, they still have geometries and configurations which can unduly stress the worker.
Accordingly, it is an object of the present invention to go beyond the use of intuitive ergonomic design techniques and to employ electrophysiological monitoring devices, such as surface electromyography apparatus, to assist in better, more appropriately informed ergonomic design of workstations to maximize the efficiency of muscle loading and thus reduce the potential for fatigue and stress and thereby contribute to the reduction and prevention of worker injury vulnerability.
Another object of the present invention is to provide a biofeedback method and apparatus for designing the human operator interface of manufacturing workstations at which repetitive tasks can be performed that are ergonomically enhanced and produce reduced muscle loading during performance of tasks at the workstation.
Still another object of the present invention is to customize an already electrophysiologically designed workstation to better adopt the human operator interface to the bodily dimensions of the individual worker so that the individual worker can adjust the interface to his or her particular physical stature.
Still a further object of the present invention is to provide an apparatus and method for designing a workstation which can accommodate workers of a widely varying physical stature, is adaptable to a wide range of different types of workstations and repetitive tasks, can be employed in rehabilitative situations, can be used as a screening test to avoid misplacement of workers and is capable of achieving substantial economic savings for the employer, as well as enhancing worker morale and physical well-being.
The apparatus and method of the present invention has other objects and features of advantage which will be described in more detail in the following Best Mode Of Carrying Out The Invention or will be apparent from the accompanying drawings.
The method of designing a workstation of the present invention is comprised, briefly, of the steps of determining a plurality of muscle loading profiles for the muscles of a worker using biofeedback or electrophysiological monitoring apparatus, such as surface electromyography apparatus, while the worker is performing a task at a workstation for a plurality of different worker/workstation relative positions; and selecting a worker/workstation relative position for extended use by the worker based upon the one of the plurality of relative positions producing substantially the lowest muscle loading profile for the worker during the determining step. In the preferred method the determining step is accomplished by varying the physical geometry in terms of the location of critical operating fixtures at the workstation so as to change the relative position between the worker and the workstation during performance of the task at the workstation. The determining step further is preferable accomplished by securing a plurality of electrical muscle load sensors (electrode pairs) to monitor muscle activity of the work when performing the task at the workstation and monitoring the muscle load sensors to generate the muscle loading profiles.
The apparatus for designing a workstation for use in the performance of a task of the present invention is comprised, briefly, of at least one electrical biofeedback sensor formed for attachment to a worker for sensing muscle loading of a muscle of the worker. The most preferred sensor embodiment employs two spaced apart electrodes attached to an individual muscle along with a grounding electrode, which are responsive to sense micro-voltages produced by the worker""s muscle during loading to produce a sensor output signal. A signal processor is electrically connected to the sensor and formed to process output signals from the sensor to produce a muscle loading profile during performance of the task by the worker. Finally, a workstation having an adjustable physical geometry capable of variation of the manner of movement of the worker""s muscles during performance of the task. In the preferred apparatus the signal processor includes appropriate programs that perform data analysis, a storage device, and a display device electrically coupled together, with the storage device being formed for storage or a plurality of muscle loading profiles therein and the display device being formed for display of at least one muscle loading profile thereon.
In the present method a test worker, and most preferably a plurality of test workers, are selected to perform the task. The test workers may have short, medium and tall physical statures to cover a range of statures for production workers who will use the workstation. Moreover, the present method further includes the step of customizing the workstation geometry further by using electrophysiological monitoring apparatus and the specific workers who will use the workstation under production conditions.